Kenwood L-07MII Power Amplifier Repair and Restoration
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- Опубліковано 5 вер 2024
- Being one of my biggest restoration jobs to date, this beautiful pair of Kenwood L-07MII amplifiers needed a lot of work. Virtually no stone was left unturned. Everything from rear I/O connector replacement to the replacement of almost every capacitor. Also addressed were the issues pertaining to the stability of the high speed circuit. Specialized care and maintenance like this is seldom found, and is never cheap. This job took hours and hours, and I tried my best to condense what was done down into a video for UA-cam.
Thanks for watching, please let me know what you think! Don't forget to like and subscribe for more content like this!
EDIT: A kind person from another form (Restorer-John) brought my attention to the full power test, stating that the output power I achieved was low, and that the asymmetrical clipping was also not normal. I set the amplifiers back up on the bench and retested at full power. This time, both amplifiers achieved 190W/8r @ 1KHz, and 294W/8r @ 1KHz. Also, no asymmetrical clipping was noted. I’m not sure what happened on the video, but if you video something like this, chances are that Murphy’s law will kick in and screw things up. Sorry for the confusion, and thank you John for bringing my attention to this!
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Relevant links for the Kenwood L-07M / L-07MII:
The Vintage Knob:
www.thevintagek...
Audio-Database:
audio-database...
HiFiEngine:
www.hifiengine...
"Black flag" polystyrene capacitor replacement information:
conradhoffman.c...
If only I could send you mine.. Ao. Scared for my own project. You did a lot lot more than just recapping and cleaning. I have no idea about all of the smaller components. I need prayers.. Lots of prayers.. Going to have many sleepless nights 😳🙄
You find the rarest items on earth! These are great amps!
Hey Connor! As soon as I had seen your new uploads , I saved them until I Had time to sit & Watch without any disturbances.I always enjoy seeing where you’re next purchase or project takes you. You have great taste & your Workmanship is impeccable. 🎉🎉🎉With all the craziness going on in the world right now ,viewing you’re content & similar is like meditation for me. Good Music , Good Sound & finding & playing on decent components is like my therapy to escape the daily rat race. 😊
Thanks for the kind comment and continued support! Glad you enjoy my videos! There will be more to come soon.
@@PrimeHiFi I'll look out for them Connor! 👍🏻😃🎉
This not only time consuming but with lots of capabilities and knowledeges. Good jobs. Thanks for sharing.
I just finished restoring something similar with same transition from to-3 to to-3p - Sansui AU-X1. I have all 12 original to-3 but didn't want to risk using them. The sound this amp produces is ..... speechless
Wish Kenwood still made amps like this. They were a fabulous manufacturer.
Young man..mad respect to guys like u..this is becoming A lost art.. I have a couple of brothers that are also really good at doing this stuff.. awesome video.. thank you for it.. keep up the good work...
Thanks for the kind words. Glad you enjoyed it. There will be more soon!
Japanese AMP on 120 V is a museum
Multi phase is the solution!
👍👍😎✌️🤟 ⭐️⭐️⭐️⭐️⭐️. Better than new. Wish you were located near me! Love to have some old favorites renewed.
Awesome work on all fronts, Connor! From the restoration itself, to the camerawork and insight you provided about the amps and process. Your best work to date, can't wait for more.
Thanks homie ❤
I have had many, and I mean many of these amplifiers... they are fantastic. Unfortunately, the MMII are the worst of the bunch given their defects.... but its great to see that you have come up with a solution for servicing and repairing them. This looks better than new. Over the years the MKI amps were the ones I held onto the longest because they did not suffer from these defects. I was fortunate enough to also own several L09M amplifiers which were built like tanks, but I eventually sold them as they did not perform well at low impedances. L07/09 are absolutely fantastic amps though, if only there were more qualified/skilled technicians out there capable of servicing them..... and enough people with fat enough wallets willing to pay. Really great work though, impressive!
Wizard!! The high power transistor replacement. A beautiful device. Thanks for sharing!
Thanks for watching! Cheers!
Fabulous work as always. Can't wait to hear a pair myself.
Thanks homie. Soon!
Love the amp and the construction. Pretty unique for its time. You restoration job also superb.
Thanks! Glad you liked it.
Hey Connor, this is impressive, I wish I had your knowledge and skills.
Thank you Thomas! That means a lot. I’ve watched your videos for a long time now. Cheers!
Amazing,its good to know theres craftsman like you,all that effort and UPS will drop it anyway
I'm lusting for these that I don't really need and probably can't afford. Great work my friend.
Great video covering the LO7's. I rebuilt a pair of these a couple of months ago and mine did not have the black flag capacitors just had standard polystyrene types. They are an interesting design construction wise and I found them easy enough to work on. I did find some of the original electrolytic capacitors were actually starting to leak out around the pins (The LO7 preamp was quite bad in some areas due to these caps leaking not to mention that dam glue and this was loaded with blackflags) I love your TO3P modification thats so ingenious and looks very professional. I have I've been restoring vintage audio for years and a new sub to your channel. You do some amazing work and look forward to future videos. All the best! 👍
I've been wanting to work on a pair of these myself so, I really appreciate seeing that you've gone through the process. It looks relatively straightforward but.. it's just so much work! Thanks for taking the time to document. I'd be curious to find out how much you paid for all the parts and such. If you had a bill of materials that would be amazing. Your friend is lucky guy.
Glad to hear you enjoyed it and found it helpful! That’s why I make these videos. Parts cost for these was roughly $500 including the high end inputs and outputs that were retrofitted. I don’t have a parts list available, but the service manuals are readily available online in which you can find every part needed. Cheers!
nice work on the power transistors on the heatsink
Que Hermoso Amplificador de potencia, Kenwood,Es una gran marca de AUDIO,Lastima que en América latina no llegaban ese tipo de línea,Solo conocí Amplificador receivers,Minicomponentes,car AUDIO o Estereos.Gran trabajo de restauración,felicidades
Such amazing workmanship! A true master! I need my nad 3020 restored but I live in South Africa! But man, I want you to do my restoration
Great restoration video. Very thorough overview of the restoration. It's great to see all the details involved. I like the hifi stand at the end. Very fine - very stylish.
Thank you!
Nice work. I had a pair when they were relatively new, way back when. They did sound good, when they worked. I don't remember how many times I had to fix the POSs. I traded them in and good riddance. Don't worry, they won't let you down. They'll break again soon enough.
Awesome video !
I have 2 pairs at home waiting for restoration... Can't wait to start the work...!
You are inspiration to me ! Thanks !
Thank you! Glad you enjoyed the video. It’s what keeps me motivated to upload. Good luck with your pairs!
Raleigh and Spencer sounds really good on your system
5:03 That's a brilliant idea!
Beautiful work man. It makes me wish I had learned to do stuff like this when I was young given my interest in HIFI. Lol, oh well.
Nice! I like demo,you should always record demo ! sound is really, really good!
Foxwarren. Good Album. Nice job.
Restored a reVox A740 this week. So satisfying to work on nice gear.
In my minds eye this what I envision when I take my vintage electronics to be repaired and calibrated! But in my heart I feel some soldier monkey just sprayed deoxit in to the pots and cleaned up outside and charged me $300.00 and call it repaired! That type of repairs & replacements are worth every penny! Like a good mechanic they're what ever they charge? Plus a tip! Great sound! That's why I love the vintage stereo equipment! Thanks gonna play the music again! Funny I just bought a used Kenwood dual Cassette player w/auto reverse out a Goodwill bin for $3 or $4 plus some other junk I don't need! And played Cassettes today in both sides and played & sounded like a champ! I forget about the Kenwood quality in their vintage stereo equipment ?!
Wow excellent restoration! Thanks for the painstaking effort on documenting your excellent workmanship!
Glad you enjoyed it! Thanks!
👍 from the 🇬🇧 excellent video and workmanship
Oh gosh so much love and dedication like it was yours! Love it man! I wish I was that friend of yours. Kudos to you!
Restoration is back breaking job, well done 👍
Nice!
Good work. Your explanation is zen for my mind. Congratulations from Portugal. 🇵🇹
just found you channel. good work I will be back
If i may ask, how much does a restoration job cost? This is really good work.
Repair and restoration prices are established on a case by case basis. Good work isn’t cheap and cheap work isn’t good 😊 Thanks!
@@PrimeHiFi while not exactly the same, I collect antique books, some centuries old, and i always bring them in to this library that does book conservation. I'm always amazed at how amazing the books turn out after conservation. This has a similar feel to it. You're definitely right. Good work isn't cheap and cheap work isn't good.
Wow amazing !!!!
$2500 on ebay
200.00
Nice job! Great info if I get around to doing mine. At least I know to replace the Black Flags before I power them up again! Thanks for the video!
Good luck with yours! Glad you found the video helpful 😊
Thanks for a great fix!
Nice work Conner, your an artist
Thank you! Cheers!
Very professional work
I have the same Chraftsman Machinists tool chest. Bought it in 1977.
Amazing work as always. Luv to see videos like this
Thanks boss
TORIO L-07MⅡ very nice sound.
I don't know where you live, but I wish you were close to my location. Amazing work.
Thank you!
Nice job, they look great 😀😀
Insanely beautiful
Best hifi restoration channel on youtube By Far. Detailed explanations, well shot, and immaculate work station. Connor, how does one acquire the skills and expertisd to diagnose and repair these electronics? Are you an electrical engineer by background? Thanks
Thanks for the kind words Chris. I’m slowly trying my hand at making videos like this. I have some bugs to iron out, but judging by the feedback so far, I must be doing something right. I am not an electrical engineer, but I have been interested in electronics for as long as I can remember. I started working on my own equipment a few years ago and slowly started to take in work. I am an aerospace engineer / A&P full time and do this work on the side.
@@PrimeHiFi Wow this is a side job !?! ...Simply amazing !!!
@@PrimeHiFi outstanding. I look forward to watching and learning from future videos. Thanks for the time and effort you put into these.
i heard if you have 20+ years car/truck, you need to replace the cap in the ecu. glad someone went through labor intensive work.
21:33 Couldn't the high speed TO3s be replaced with lower speed TO3s saving all that trouble? Was the high speed necessary to the circuit? Presumably, if speed was not needed, lower speed transistors might not go into high frequency oscillation in the first place, right?
Kenwood applied feedback well above the audible band. The high speed nature of these amps doesn’t only come from the high fT outputs, rather the circuit as a whole. Replacing high speed semiconductors comes with the possibility of hurting the performance of the amplifier and can even lead to other issues as well. Putting the amps back together with parts similar to what were used when they were designed is the way to go.
@@PrimeHiFi Ah that makes sense then. Thank you for sharing this.
Saludos, máquinas soberbias, verdadera Alta Fidelidad, nada que ver, con las mentiras actuales del High End, gracias por compartirlo, abrazos desde Bogotá, Colombia...
What incredible work. Hat off to you sir. Love the music at the end too. Who is it?
Stellar job.
Wow.
Excellent job.
You r a real Pro.
Very nice and comprehensive video ... Awesome work Brother ... 😎
Beautiful work, well done!
Good engineering work...well done...however the camera work makes me feel like Iv'e just got off a roller coaster...LOL
Hey, great video, thanks you for sharing
What an awesome Job!
Very impressive.
great setup !
Very nice work and it is great to see a fully restored set. I owned the whole LO7 set back in the day and used to sell them. The amps where fantastic sounding but they tended to run hot, especially the LO5s . We had very high failure rates and durability issues but boy did they sound good. In this series the amps were fantastic , the pre amp middle of the road, and the turntable was without question fabulous and I think the best of the series.
PS Do you have a repair shop?
Thanks for the kind comment! Yes! I’m well aware of the stability issues of these amps. The issues mostly stem from the factory QC and a select few components that end up drifting overtime, killing the amplifiers. It’s a shame, as most of the series suffered a terrible fate because of it. I run a small HiFi equipment lab on the side, yes!
Like a pro.! Awesome job.! 👍
Great work!
very nice job Connor!
Thank you!
Nice amplifiers, it's a shame they have so much design flaws... Nice restoration BTW
Excellent!👌
Very nice work your doing!!
Great Job ! Thanks for the video Top Level !!!!!
very clean and nice work
I believe that it is doing crazy things to your system because of the DC coupled design with no caps in the signal path. I have a KA-7100 DC integrated with 60 wpc. They like to call it mid-fi but it does things I never heard any amp do at multiples times its price. I never believed or understood the concept or "pace" until I heard this amp. The mixing of the original recording of take 5 by Dave Brubeck made no sense until I heard it through the 7100. Would love to hear these amps. You did a great job. Whatever it cost, (assuming not gouging) it is worth it. Would love to own a pair myself.
Super , excellent 👏 👌 👍 🙌 ❤❤
Damn....you got Talent...very nice presentation.... !
Thanks for sharing this video Dude ❤
6:25 This is the most surpising thing I've learnt from this video. I never thought a restoration would result in polystyrenes being replaced by ceramics. Is it just the polystyrenes that are temperature sensitive, seeing that a lot of mylars are still left in there?
Yes, the “black flag” polystyrenes used in many of the high speed amplifiers in the 70’s and 80’s must be replaced to prevent oscillation. They are nasty and drift with age. See here: www.conradhoffman.com/BF_caps.htm
@@PrimeHiFi Thanks for the link! It's been some time since I last visited that site. I had forgotten about these. It seems one would provide a great service by cataloguing all those aging components (caps, resistors, semiconductors etc.) in one site. Professionals in the trade of restoring probably know them by heart but it would make a useful reference for hobbyists that unwittingly plug an old piece just acquired in the mains only to watch a puff of smoke be produced from it.
Beautiful work!!!
Great job man...congrats !!!
Dear Connor, great job indeed. As introduction, Can you add a short movie related on how to remove the top cover ? Cheers, Massimo
Glad you enjoyed the video! Please reference the service manual for complete disassembly instructions. The service manual offers comprehensive instructions with clear pictures on how to do this. It is available on HiFiEngine
It's like working on your
car. Mechanics go through the same thing.
It takes a long time to put it together.
I have a pair of L-07M (first iteration), they are very good sounding amplifiers. I have a 3rd one that doesn't work, one of the screws on the top is gutted out and I can't unscrew the top. I have no idea what's wrong with it, but I have a feeling it's a bad relay.
Nice job remounting the TO3P devices, the axial capacitors on the protection board would benefit from the application of a soft adhesive or silicone sealant (Dow Corning RTV3140 does not contain acetic acid) to prevent the soldered connections from failing due to vibration of the capacitors.
Thank you! And yes, I always add a bead of thermoplastic glue to components like this. I ended up doing it after taking the video. Cheers!
Very well done!!
Beautiful work. I have a pair of the MkIIs myself. Do you have a list of parts and where you got them that you could post?
Thank you! I don’t have a parts list, but they can be found in the service manual which is available online.
nice work man 👍
Is it fair to say you specifically is integrated and power amps?
Kenwood, une grande marque Japonaise, qui n'a rien à envier à Pioneer, Sansui, Sony, Technics, Yamaha, Sony, et autres.
Dans les années 80, j'avais le couple Basic C2-M2, un très bel ampli, impossible à mettre en défaut.
Dommage que certaines de ces grandes marques aient disparu de la hifi de qualité, alors qu'elles étaient d'aussi bonne facture... 🥲
are they worth the restore as i have ken L0-5 dont how much will it coast to rebuilt it back
AMAZING work my friend excellent note to detail which is hard to find nowadays. I’ve got a klipsh synergy 10 subwoofer and I blew the fuse on it unfortunately I had lost the fuse and the cap that screws on it I guess l should I try contacting Klipsch any thoughts ? Thanks
Thank you! Yes - that will be your best bet. Or bring it to someone local to you to have it repaired.
Nice video sir
Cost to replace everything in the stereo amplifier.
Would you like to restore a Marantz 2325 reciever? Hey l know good work when l see it, and l must say it doesn't look cheap
With the current supply chain issues any problem getting supplies?
What an incredible sound! What kind of speakers are you playing in this video? They really sound awesome!
Thanks! They are Vandersteen 2Ci
I found changing the output transistors totally changed the sound of my power Amp - not for the better.
It was just not the same - such a shame, it ruined the Amp.
@@ericschulze5641 1 was blown and no replacement available.
14:40 The design engineer obviously did not think this through and, I guess, the assembly technicians either never went back to complain or were ignored. I mean, how on earth are you supposed to solder a big slab of copper onto a copper track? The designer should have opted instead for either a conductive screw (probably a bad choice) or a cable or some sort of combination e.g. a cable with crimped eyelets that are then screwed on to make a sturdy connection. - which is a very common solution. What on earth were they thinking here?
I think, all too often style takes over proper engineering and that can only have one outcome.
18:01 This is exactly what I meant: a much better solution, mechanically, electrically and easier manufacture-wise.
But why were the two ground wires at 18:20 also connected to the copper sheet? I mean what's the point of the copper sheet then? There might as well be only ground wires all connected to the same screw on the chassis. This copper bus plus ground wires solution is neither here nor there and I fail to see any benefit.
19:11 So is this varnish thing found everywhere just left over flux? I always thought this was some sort of moisture-proofing varnish used in all old electronics! If it's flux, then must we remove it? and how? Once this is removed, is there something to protect bare copper tracks from corrosion (as in modern pcbs)? Or do we just have to cover them with solder (which is both laborious and very risky on old pcbs)?
The material on the back side of the PCB that covers the solder mask is flux. The flux attracts dirt and dust, and can become corrosive and conductive overtime with moisture. Added to the fact that it could mess with high impedance circuits, I always remove all flux from PCB’s.
@@PrimeHiFi I later realised while watching that these pcbs where already coated anyway, i.e. the copper tracks were not exposed to air. Pretty strange for a prestigious manufacturer to leave flux on their boards in their flagship component. I guess back when it was it made they had not had components with pcbs go bad yet as pcbs had been in use for only, what, two decades? I wonder whether this thing had been hand-soldered. I guess it was.
What kind of music did you listen?
What's your opinion on the Revox B242 amplifier ?
Amazing job